1. Field of the Invention
The present invention relates to a common rail in a Diesel internal combustion engine, such as a main pipe rail comprising a manifold or a block rail for high-pressure fuel, fastened and jointed by a branch connector such as a branch pipe or a branch fitting.
2. Description of the Prior Art
In one of this kind of joint structure for a common rail of the prior art, as shown in FIG. 9A, a main pipe rail 11 is known; a branch hole 11-2 of a circular section formed in the circumferential wall of a main pipe rail 11 of a circular section and communicating with an internal conduit 11-1 of a circular section is formed to have a pressure receiving seat 11-3 opened to the outside, and a ring-shaped joint fitting 13 enclosing the outer circumference of the main pipe rail 11 in the vicinity of the pressure receiving seat is used to bring a pressure seat 12-3, which is formed by a joint head 12-2 of a branch pipe 12 as a branch connector tapered by the buckling method, into abutting engagement with the end portion of the pressure receiving seat 11-3, so that the branch pipe 12 is jointed to the main pipe rail 11 by fastening a nut 14, which is assembled in advance in the branch pipe 12, by pressure below the neck of the joint head 12-2 into a threaded wall 13-1 protruded from the joint fitting 13. In place of the ring-shaped joint fitting 13, as shown in FIG. 10A, a cylindrical sleeve nipple 13a is mounted so directly on the outer circumference of the main pipe rail 11 as a common rail by the welding or soldering method as to protrude radially of the main pipe rail 11, and the pressure seat 12-3, as formed by the joint head 12-2 of the branch pipe 12, is brought into abutting engagement with the pressure receiving seat 11-3 of the main pipe rail 11, so that the branch pipe 12 is jointed to the main pipe rail 11 by fastening the nut 14 into the sleeve nipple 13a. In all these common rails of the prior art, as shown in FIGS. 9B and 10B, the center of the conduit 11-1 of circular section of the main pipe rail 11 is aligned with the center of a conduit 12-1 of the branch connector 12. Reference numeral 15 designates a sleeve washer.
As shown in FIG. 11, moreover, another common rail is constructed by using an L-shaped branch fitting 22 as a branch connector between the branch pipe 12 and the main pipe rail 11. For this branch connector connecting to the common rail, the case of using the branch fitting such as an elbow or the case of using the branch fitting equipped therein with an equal-pressure valve, an attenuation valve, a feed valve, a discharge valve or a flow control valve is taken into consideration so as to avoid such an interference with other parts as will occur due to a large curvature of the branch pipe when this pipe is to be bent. In the common rail exemplified herein, the branch fitting 22 is equipped at its one end with a spherical pressure head 22-1 having a spherical pressure seat 22-2 so that this pressure seat 22-2 is brought into abutting engagement with a pressure receiving seat 11-3' at the main pipe rail 11 by screwing a threaded face 22-3 formed in the outer circumference of the branch fitting 22 into a threaded face 13'-1 of a joint fitting 13'. To the other end of the branch fitting 22, there is connected by the branch pipe 12 which is fixed by screwing a cap nut 24 through a sleeve 25. According to this construction, the branch pipe 12 can be led out in parallel with the axial direction of the main pipe rail 11.
In the common rail of the prior art having the structure in which the branch hole 11-2 having the circular section is mounted on the main pipe rail 11 as a common rail having the circular section in alignment with the center of the conduit 11-1 of circular section of the main pipe rail 11, however, the maximum stress is established at the open end P of the main pipe rail passage 11-1 of the conduit 12-1 of the branch pipe 12 as a branch connector when the internal pressure acts upon the main pipe rail 11 so that a crack is liable to start from the open end P to invite the fuel leakage.